By way of background, radiation curable adhesive compositions are well known in the art as exemplified by U.S. Pat. No. 5,104,921 to Erickson et al.; U.S. Pat. No. 4,483,951 to Brenner; U.S. Pat. No. 5,695,837 to Everaerts et al.; U.S. Pat. No. 5,747,551 to Lewandoski et al.; U.S. Pat. No. 5,284,091 to Kon et al.; U.S. Pat. No. 5,244,962 to Plamthottam et al.; and U.S. Pat. No. 4,952,435 to Okita. These patents disclose adhesive compositions wherein at least a portion of the composition is cured or cross-linked by the application of radiation generally in the form of ultraviolet radiation or electron beam radiation.
The trend in the adhesive coating industry has been to move towards adhesive compositions which are solventless. The Brenner '951 patent exemplifies this movement towards the use of adhesive compositions containing no solvents. The elimination of solvents eliminates air pollution problems, solvent toxicity problems, and can also offer both energy and labor saving since solventless adhesive compositions are capable of curing in much shorter time periods than solvent-based adhesive compositions and can also be cured without the application of external heat which can cause damage to the underlying article or substrate.
The Brenner '951 patent discloses adhesive compositions which are comprised of an elastomer, a chemically compatible ethylenically unsaturated monomer, a tackifier, and an adhesion promotor, and optionally, pigments, fillers, thickeners, and flow control agents, which are converted from the liquid to the solid state by exposure to high energy ionizing radiation such as that from an electron beam. The constituents of the adhesive compositions disclosed in the Brenner '951 patent are common to this class of adhesives, that being, a polymerizable monomer component, an elastomeric component, and a tackifier.
The composition disclosed in the Brenner '951 patent are taught as being primarily useful as an adhesive for the assembly of composite structures or laminates of, for example, a rubber sheet and a metal base. The adhesive composition can be applied to the elements comprising the composite laminate structure and then the laminate can be built up upon the adhesive layers. The laminate is then subjected to an electron beam to cure the adhesive composition. While certain manufacturing or processing schemes may be adequately accomplished using a radiation cured polymer composition such as that disclosed in the Brenner '951 patent wherein the adhesive composition is applied to the components to be adhered together and thereafter the components are irradiated to cure the composition, there exists a need for a radiation cured, heat activated adhesive coating which can be applied to a multiplicity of articles, cured by the application of radiation, the coated articles then stacked or rolled upon each other without adhering to one another, and the coating can later be activated by the application of heat to allow the coated articles to be adhered to a desired substrate.
The prior art is devoid of any teachings or suggestions for an adhesive composition which can be applied or coated onto a multiplicity of articles, the articles then being radiation cured, and then stacked or rolled upon one another without forming a block or adhering to one another at room temperature thus becoming useless for their designated purpose. While the prior art teaches a number of radiation cured adhesive compositions, the prior art does not disclose an adhesive composition which, after being radiation cured, is non-blocking at room temperature and which remains heat activatable to allow a coated, cured article to be affixed to a substrate upon the application of heat thereto.
Accordingly, it would be advantageous and desirable to have a radiation curable coating composition for the preparation of a non-blocking, heat activatable heat adhesive which, following radiation curing, is non-blocking at room temperature but which also remains heat activable and able to subsequently become adhesive.